This invention relates to a high-voltage switching installation insulated by compressed gas and having a metal encapsulation, several sections of the encapsulation being partitioned-off gastight by means of bulkhead bushing insulators.
As described in U.S. Pat. No. 3,887,915, a monitoring device responding to interference arcs can be associated with such an installation, the monitoring device containing sensors which can be mounted on the outside of the encapsulation and producing a signal which is fed to an evaluation device. The monitoring device can be connected permanently or only temporarily to the installation for checking the operating state of the system. The known monitoring device includes acoustic sensors, namely, electroacoustic transducers in the form of sound microphones, which are arranged on the outside of the encapsulation for detecting sound waves transmitted through the solid material of the encapsulation. These electroacoustic transducers are always arranged adjacent to a bulkhead bushing insulator which defines a gas space in the encapsulation. This positioning of the transducers enables a determination of the gas space in which the interference arc occurs. In the known monitoring device, the signals of the sensors are fed to an evaluating device which contains amplifiers, frequency and amplitude-dependent filters and a timing device as well as a signaling or indicating device. This special design of the evaluating device picks up, due to the limitation to a given frequency or amplitude range, only the characteristic noises of an arc developing due to an electric breakdown, the main component of which has twice the network frequency. In addition, only those signals are amplified which have a minimum amplitude, so that interference signals below a given level are not evaluated. The known evaluating device further takes into consideration the fact that arcs occur also during normal operation of a high-voltage switching installation, namely, when circuit breakers are switched under load. The timing component of the evaluating device passes the signals corresponding to an arc only if the signal is longer than the quenching time of the circuit breaker. In this manner it is assured that the evaluating device responds only to interference arcs and does not evaluate the switching-off arc of a circuit breaker.
In networks which include, besides overhead lines, also high-voltage switching installations which have metal encapsulations and are insulated by compressed gas, a normal, automatically operating network protection system is provided. This network protection system would respond also in the event of grounds and shorts in the switching installation and, as is common in overhead lines, cause reclosing in accordance with a predetermined system of staggering. In overhead line systems a brief interruption can cause the interference arc to be switched away, but in an encapsulated high-voltage installation, this effect practically does not exist so that the interference arc would be restarted and cause a further pressure rise in the gas space involved.
The disturbances related to arcs within a high-voltage switching installation can damage or contaminate parts of the installation. This possibility of damage results in the need to switch off individual sections of the encapsulation or gas spaces after disturbances and eliminate the pressure, so that repairing and servicing work can be carried out in the gas-containing compartments. Also other repair work or work for enlarging such an installation can require the partial disconnection and opening of existing system.
The boundary surfaces of the partitioned sections of the encapsulation or the gas spaces are the bulkhead bushing insulators. Generally, the bushings consist of plastic such as cast resin with an epoxide-resin base and are designed to withstand with sufficient safety margin the mechanical stresses arising in normal operation, including internal interference arcs when the entire metallic encapsulation is closed. In this way, the effect of an interference arc is limited to the gas space concerned. In servicing, however, a bulkhead bushing insulator may form a terminating wall element of the encapsulation which is freely accessible from one side and is acted upon only one side by the normal operating pressure of the insulating gas, the counter pressure of the otherwise adjacent gas space being absent. As a result, the unilaterally exposed bulkhead bushing insulator is mechanically stressed to a higher degree than in normal operation by a pressure rise due to an interference arc. If maximum current and a long burning time of the interference arc coincide, it can not be precluded that the bulkhead bushing insulator might burst due to the pressure increase, creating danger to the installation personnel.